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The paper describes the development and application of physical-financialmodelling techniques to the analysis of relations between development design –covering the broad characteristics of a scheme, such as land use mix, developmentdensity and built form – and financial viability. It is divided into two parts

useful resource for the creation of more detailed real time models of the new site within the larger scale visualization model.

There are many 3D CAD systems available that could be used in the ways described in this chapter. However, any such system had to be compatible with Simmetry3d, the system used for the real-time visualizations, in terms of the format of models that could be imported. This restricted the choice of CAD system. SketchUp was identified as the most suitable because it could achieve the requirements already outlined, was perceived to be easy to learn and to use, and was compatible with the visualization system.

The categorisation of the design elements was achieved through SketchUp’s ‘layering’ system. Layers were added that corresponded to the categories required by the financial appraisal spreadsheet. These categories were: site, hard landscaping, soft landscaping, roads and footpaths, car parking, building floor and use (for example, retail, offices and so on). Practically, this means that each design element, for example, a part of a site or a floor of a building, is assigned to the layer that best describes its use, such as soft landscaping or apartments.

The link between SketchUp and the spreadsheet package required a plug-in to be written that analysed the 3D model based on layer categorisation. This analysis computed the land use area (square metres) of the design according to the pre-defined categories. These layer categories correlated to categories in the targeted spreadsheet that computed the financial implications of the design. The user may run the plug-in whenever a financial appraisal is required. For example, when a design has been successfully input and categorised, or when changes to the design or categorisations are made. The overall structure of the modelling system is described in Figure 2.

Figure 2: The Physical-financial Modelling System

Preparation of a design in SketchUp typically involves the following steps:

1. The creation of a 2D site plan.

2. The categorisation of areas within the site plan.

3. The extrusion of 2D building areas into massing models (that require each floor of the building to be included too).

4. The categorisation of the floor space within the extruded buildings.

Creation of the site plan was most easily and accurately achieved by using (importing) GIS land-use data (OS MasterMap dataset) that covered the whole site and accurately defined the site area. Existing detail within the site could easily be removed and re-modelled using the tools available within SketchUp. As already indicated, models constructed in this way could be imported into a larger scale, more detailed